(1) Field of the Invention
The present invention relates to a rotary cutting die assembly and its method of construction. In particular, the present invention relates to a rotary cutting die assembly comprising a support roll supporting a floating sheeter blade and a lock-down bar assembly that secures the sheeter blade to the support roll, in addition to the method of constructing the rotary cutting die assembly.
(2) Description of the Related Art
Prior art rotary cutting die assemblies employed in sheeter operations, i.e. the cutting of sheets of material from a web of stock material, commonly employ a rotating cutting die cylinder supporting a sheeter blade. The cutting die cylinder and a rotating anvil roll are typically mounted parallel to and adjacent each other on a rotary press. The cutting die cylinder and anvil roll rotate against each other as the web of stock material is passed through the press between the rotating die cylinder and the anvil roll. A pressure assist roll or a load carrying truck or tractor assembly is often employed to exert a downward force on the rotating cutting die cylinder causing it to bear against the anvil roll. As the web of stock material is passed between the rotating die cylinder and the anvil roll, the sheeter blade mounted on the die cylinder cuts the web of material into individual sheets. The size of the sheets produced corresponds to the axial length of the cutting die cylinder and the circumferential distance over the exterior of the die cylinder between adjacent sheeter blades mounted on the cylinder.
The cutting die cylinder of rotary cutting die assemblies of the type used in continuously cutting sheets of material from a web of stock material are commonly formed from a solid steel cylinder. The cutting die cylinder is formed large enough in diameter to provide a circumferential distance between a sheeter blade, or blades, mounted on the cylinder that corresponds to the desired length of the sheets to be cut from the web of stock material. The diameter of the cutting die cylinder is also chosen to provide sufficient strength to the cylinder to prevent any deflection of the cylinder during rotary cutting operations of the press.
The cutting die cylinder is formed with journal shafts protruding from its opposite ends. The journal shafts are used in mounting a gear on the die cylinder, and for rotatably mounting the cylinder in a rotary die cutting press. The gear mounted on the die cylinder meshes with a gear on the anvil roll of the press to deliver a rotational force to the cutting die cylinder and to maintain the die cylinder, the anvil roll, and other operations performed by the rotary cutting press in synchronism.
The cutting die cylinders of prior art rotary cutting die assemblies are typically formed from metal bar stock on a lathe. An axial slot is provided in the surface of the cylinder to receive the cutting blade. In one type of cutting die cylinder, several tangential notches are milled into the cylinder exterior surface adjacent the axial slot. The notches are spatially arranged along the length of the slot and are formed in the cylinder with flat base surfaces that are oriented parallel to the sidewalls of the axial slot. A threaded hole is formed through the base surfaces of each notch and into the slot. Set screws are threaded into the holes and are tightened down in the holes to engage the cutting blade received in the slot and thereby secure the blade in the slot.
Cutting die assemblies of the type described above have been found to be disadvantaged in that several different forming steps are required to construct the die cylinders of the assemblies. The method of constructing the die cylinders is both time consuming and expensive, and requires expensive metal working equipment and skilled laborers.
Rotary cutting die assemblies have been developed in the prior art seeking to reduce the number of forming steps, shortening the manufacturing time, and reducing the equipment and labor required in making the die assemblies. A typical example of this type of prior art rotary cutting die cylinder assembly is disclosed in U.S. Pat. No. 4,715,250. This type of rotary cutting die assembly comprises a die cylinder that is also formed on a lathe. A plurality of longitudinally spaced grooves are formed in the circumference of the cylinder on the lathe. An axial slot is formed in the cylinder traversing the plurality of circumferential grooves. The slot is dimensioned with sidewalls spaced wide enough apart to receive a cutting blade, a stiffening shim, and a mounting bar.
The mounting bar has a rectangular cross section and a plurality of set screws received in threaded holes in the bar at axially spaced intervals along the bar. The circumferential grooves formed in the circumference of the cylinder have an axial spacing complementary to the axial spacing of the set screws in the bar so that a tool can be inserted into the circumferential grooves to tighten and loosen the set screws with the mounting bar received in the axial slot. When the set screws are tightened, they push the cutting blade and mounting bar against the opposite sidewalls of the slot, thereby frictionally engaging the cutting blade and mounting bar in the slot.
Although the rotary cutting die assembly described above is an improvement over earlier die cutting assemblies in that it requires fewer machining steps and correspondingly is less expensive to produce than other cylinder assemblies, the method of forming the die assembly still involves a number of machining steps in forming the axial slot in the surface of the die cylinder and in forming the plurality of circumferential grooves around the surface of the die cylinder. Accordingly, it would be advantageous to provide a rotary cutting die assembly that is produced according to a method that requires a reduced number of machining steps and thereby reduces the time and expense involved in producing the die assembly.